The present invention relates to a non-contacting information card for use as commuter's tickets, management cards for animals and lift tickets for a skiing ground and which can transmit and receive information to and from a card reader/writer by radio waves.
Non-contacting information cards which can transmit and receive information, such as identification (ID) number, due data and the number of times, between it and a card reader/writer via radio waves have recently been used as commuter's tickets, management cards for animals and lift tickets for a skiing ground, for example.
While the non-contacting information cards have heretofore been operated by a battery, in order to reduce the thickness of the non-contacting information card and to facilitate the management of the non-contacting information card, proposed non-contacting information cards are not operated by batteries but they can be operated by a voltage which results from rectifying a carrier signal used to transmit information from the card reader/writer.
FIG. 1 of the accompanying drawings shows an example of an information card system using a non-contacting information card which is not operated by a battery. This information card system will be described below with reference to FIG. 1.
As shown in FIG. 1, fundamentally, the information card system is composed of a non-contacting information card 1 and a card reader/writer 2 for transmitting and receiving information between it and the non-contacting information card 1 via radio waves.
As shown in FIG. 1, the card reader/writer 2 includes a main control unit 21 consisting of a CPU (central processing unit), a signal input terminal 22, a signal controller 23, a data buffer RAM (random-access memory) 24 and a high-order interface controller 25. Transmission information from the main control unit 21 is supplied through a PS/SP (parallel-to-serial/serial-to-parallel) converter 26 which converts information supplied thereto in the parallel to serial form to a FSK (frequency shift keying) modulator 27.
The FSK modulator 27 sets a frequency f.sub.1 to 320 kHz, for example, when a digital signal is at high "1" level and sets a frequency f.sub.2 to 280 kHz, for example, when the digital signal is at low "0" level. The card reader/writer 2 shown in FIG. 1 further includes a reference oscillator 28 and a frequency divider 29 which divides a reference signal supplied thereto from the reference oscillator 28 to obtain the signals with the frequencies f.sub.1 and f.sub.2.
An output signal from the FSK modulator 27 is supplied through a low-pass filter (LPF) 30 and an amplifier (AMP) 31 to a coil 32 which forms a write head.
As shown in FIG. 1, the card reader/writer 2 further includes a coil 33 that forms a read head. An ASK (amplitude shift keying) signal obtained at the coil 33 is supplied through a band-pass filter (BPF) 34 to an ASK demodulator 35. A demodulated signal from the ASK demodulator 35 is converted in the form of serial-to-parallel data by the PS/SP converter 26 and then supplied to the main control unit 21.
Further, a voltage from a commercially-available power source is supplied to an AC input terminal 36. The voltage from the commercially-available power source supplied to the AC input terminal 36 is supplied to a power supply unit 37. The power supply unit 37 supplies a regulated DC voltage which is used as an operation voltage to operate the card reader/writer 2.
The non-contacting information card 1 includes a resonance circuit 3 having a resonance frequency f.sub.0 of 300 kHz, for example, for reading out the FSK signal supplied thereto from the coil 32 constructing the write head. The FSK signal from the resonance circuit 3 is supplied through a bandpass filter (BPF) 4 to a FSK demodulator 5. Information provided in the form of a digital signal obtained at the output side of the FSK demodulator 5 is supplied through a PS/SP converter 6, which converts the information in the form of serial-to-parallel data, to a main control unit 7 formed of a CPU.
The main control unit 7 supplies a memory 8 with data, such as a read command signal and a memory information signal. Therefore, data is written in or stored data is read out from the data memory 8 under the control of the main control unit 7.
The digital signal, which is the information signal read out from the data memory 8, is supplied to the main control unit 7. The digital signal, which is the information signal read out from the data memory 8 under the control of the main control unit 7, is converted in the form of parallel-to-serial data by the PS/SP converter 6 and then supplied to an ASK modulator 9. The non-contacting information card 1 further includes an oscillator 10 which supplies a carrier signal having a frequency f.sub.3, e.g., 300 kHz to the ASK modulator 9.
An ASK signal of the information signal obtained at the output side of the ASK modulator 9 after the information signal has been read out from the data memory 8 is supplied through an amplifier (AMP) 11 to a coil 12 which transmits the ASK signal to the coil 33 constructing the read head of the card reader/writer 2 in an electromagnetic coupling way.
In the example shown in FIG. 1, the FSK signal received by the resonance circuit 3 is supplied to a rectifier 13 and a DC voltage obtained at the output side of the rectifier 13 is used as an operation voltage to operate the non-contacting information card 1.
According to the non-contacting information card 1, since the non-contacting information card is not provided with the battery, it can be reduced in thickness and becomes useful from an administration standpoint.
A power for driving the non-contacting information card 1 is transmitted from the card reader/writer 2 in the form of electromagnetic wave. Therefore, if a positional relationship between the resonance circuit 3 and the coil 32 which constructs the write head of the card reader/writer 2 is always constant, then a voltage induced in the resonance circuit 3 becomes always constant.
However, in actual practice, when the non-contacting information card 1 is in use, the non-contacting information card 1 can be moved in a predetermined area that is provided as an operation area in which the non-contacting information card 1 can come near or away from the coil 32 constructing the write head of the card reader/writer 2. The non-contacting information card 1 can be located randomly within this operation area. Therefore, when the non-contacting information card 1 is located nearest the coil 32 of the card reader/writer 2, an excess voltage is induced in the resonance circuit 3 of the non-contacting information card 1 so that the rectifier 13 outputs an excess voltage. Thus, in worst cases, there is then the risk that an IC (integrated circuit) chip or the like disposed in the non-contacting information card 1 will be destroyed by the excess voltage.
In order to prevent the IC chip or the like from being destroyed by the excess voltage, it is proposed that the non-contacting information card 1 incorporates a constant voltage controller of a serial control type in association with the rectifier 13 to dissipate an excess voltage as a heat when the output voltage of the rectifier 13 increases in excess of a predetermined value.
However, in this case, the constant voltage controller which treats the excess voltage as a heat is considerably complicated in circuit arrangement and also occupies a relatively large area of the IC chip of the non-contacting information card 1. As a consequence, the non-contacting information card becomes expensive.